finding and replacing 'nan' with a number

Question

I want to replace number 3 instead of all 'nan' in array. this is my code:

train= train.replace("nan",int(3))

But nothing changes in my array. Could u please guide me?

Answer 1

You can use np.isnan:

import numpy as np
train = np.array([2, 4, 4, 8, 32, np.NaN, 12, np.NaN]) 
train[np.isnan(train)]=3
train

Output:

array([  2.,   4.,   4.,   8.,  32.,   3.,  12.,   3.])

Answer 2

This code changes all nan to 3:

y = np.nan_to_num(x) + np.isnan(x)*3

This code changes all 3 to nan:

y = x*(x!=3) + 0/(x!=3)

These methods only work with numpy arrays. Please note that np.nan_to_num(x) always changes nan to 0.